The invention relates to nuclear magnetic resonance (NMR) spectroscopy, and in particular to systems and methods for forming demountable cryogenic NMR connections in NMR spectrometers.
Nuclear magnetic resonance (NMR) spectrometers typically include a superconducting magnet for generating a static magnetic field B0, and an NMR probe including one or more special-purpose radio-frequency (RF) coils for generating a time-varying magnetic field B1 perpendicular to the field B0, and for detecting the response of a sample to the applied magnetic fields. Each RF together with its associated circuitry can resonate at the Larmor frequency of a nucleus of interest present in the sample. The RF coils are typically provided as part of an NMR probe, and are used to analyze samples situated in sample tubes or flow cells.
An NMR frequency of interest is determined by the nucleus of interest and the strength of the applied static magnetic field B0. In order to maximize the sensitivity of NMR measurements, the resonant frequency of the excitation/detection circuitry is set to be equal to the frequency of interest. NMR experiments use information on the phase relationships between acquired data sets (vectors) in order determine a number of types of information. Such information may include spatial information, chemical shifts, and inter-nuclear contact times.
NMR systems commonly use superheterodyne-like receivers to detect the response of NMR samples to applied RF energy. During a transmit phase, a local oscillator signal is mixed with a continuous-wave or pulsed intermediate-frequency signal using a transmit-side mixer to generate a transmit NMR signal, which is applied to the sample of interest. During a subsequent receive phase, the received NMR signal is mixed with the local oscillator signal using a receive-side mixer to generate an intermediate-frequency receive signal indicative of the sample NMR response.
FIG. 1 shows an exemplary prior art NMR system 1000 including transmitter 1100 for applying RF energy to a sample coil 24, and a receiver 1200 for detecting an NMR signal from sample coil 24. Transmitter 1100 includes a mixer 1102, which mixes RF signals generated by a local oscillator 1104 and an intermediate-frequency (IF) source 1106. Receiver 1200 includes a mixer 1202, which mixes RF signals generated by local oscillator 1104 and received from sample coil 24 to yield an IF NMR signal of interest. Amplifiers 1204, 1206 are used to amplify received signals before and after mixer 1202. The IF NMR signal may be digitized and processed further to yield desired NMR data such as NMR spectra.
Such transmit/receive signal processing schemes are capable of accurately generating and detecting NMR signals of interest, which commonly have low amplitudes and high frequencies. At the same time, such signal processing schemes can add significant complexity and cost to NMR systems, and analog mixers can introduce spurs or other signal artifacts. Some multi-channel NMR systems may employ 16-20 mixers and associated cables and other RF components.